Changing effective work function using ion implantation during dual work function metal gate integration

ABSTRACT

Ion implantation to change an effective work function for dual work function metal gate integration is presented. One method may include forming a high dielectric constant (high-k) layer over a first-type field effect transistor (FET) region and a second-type FET region; forming a metal layer having a first effective work function compatible for a first-type FET over the first-type FET region and the second-type FET region; and changing the first effective work function to a second, different effective work function over the second-type FET region by implanting a species into the metal layer over the second-type FET region.

DIVISIONAL APPLICATION

This divisional application claims priority to co-pending U.S. patentapplication Ser. No. 12/190,220 entitled CHANGING EFFECTIVE WORKFUNCTION USING ION IMPLANTATION DURING DUAL WORK FUNCTION METAL GATEINTEGRATION, filed on Aug. 12, 2008, the contents of which are herebyincorporated by reference in their entirety

BACKGROUND

1. Technical Field

The disclosure relates generally to integrated circuit (IC) chipfabrication, and more particularly, to dual effective work functionmetal gate integration.

2. Background Art

The continued scaling of complementary metal-oxide semiconductor (CMOS)devices requires successful integration of dual work function metal gateelectrodes on high dielectric constant (high-k) gate dielectrics.

BRIEF SUMMARY

Ion implantation to change an effective work function for dual effectivework function metal gate integration is presented. One method mayinclude forming a high dielectric constant (high-k) layer over afirst-type field effect transistor (FET) region and a second-type FETregion; forming a metal layer having a first effective work functioncompatible for a first-type FET over the first-type FET region and thesecond-type FET region; and changing the first effective work functionto a second, different effective work function over the second-type FETregion by implanting a species into the metal layer over the second-typeFET region.

A first aspect of the disclosure provides a method comprising: forming ahigh dielectric constant (high-k) layer over a first-type field effecttransistor (FET) region and a second-type FET region; forming a metallayer having a first effective work function compatible for a first-typeFET over the first-type FET region and the second-type FET region; andchanging the first effective work function to a second, differenteffective work function over the second-type FET region by implanting aspecies into the metal layer over the second-type FET region.

A second aspect of the disclosure provides a method comprising: forminga high dielectric constant (high-k) layer and a metal layer over thehigh-k layer, the metal layer having a first effective work function;changing the first effective work function to a second, differenteffective work function in a region by implanting a species into themetal layer over the region; and forming a first-type FET compatiblewith the first effective work function over an area outside the regionand forming a second-type FET compatible with the second effective workfunction over the region.

A third aspect of the disclosure provides a structure comprising: afirst-type field effect transistor (FET) including a gate having a highdielectric constant (high-k) layer and a metal layer, the metal layerhaving a first effective work function; and a second-type FET includingthe high-k layer and the metal layer, the metal layer further includingan implanted species that changes the first effective work function to adifferent second effective work function.

The illustrative aspects of the present disclosure are designed to solvethe problems herein described and/or other problems not discussed.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of this disclosure will be more readilyunderstood from the following detailed description of the variousaspects of the disclosure taken in conjunction with the accompanyingdrawings that depict various embodiments of the disclosure, in which:

FIGS. 1-3 show embodiments of a method according to the disclosure.

FIG. 4 shows embodiments of a structure according to the disclosure.

FIG. 5 shows a graph illustrating a threshold voltage shift achievableusing the teachings of the disclosure.

It is noted that the drawings of the disclosure are not to scale. Thedrawings are intended to depict only typical aspects of the disclosure,and therefore should not be considered as limiting the scope of thedisclosure. In the drawings, like-numbering represents like-elementswhen comparing between drawings.

DETAILED DESCRIPTION

Turning to the drawings, FIGS. 1-3 show embodiments of a methodaccording to the disclosure. FIG. 1 shows a preliminary structure 100including a substrate 102 having trench isolated regions 104, 106 for ann-type field effect transistor (NFET) and a p-type FET (PFET),respectively. As understood, the position of the types of FETs may bereversed so long as they are of opposite polarity. Hereinafter, region104 is referred to as first-type FET region and region 106 is referredto as second-type FET region. Substrate 102 may include but is notlimited to silicon, germanium, silicon germanium, silicon carbide, andthose consisting essentially of one or more III-V compoundsemiconductors having a composition defined by the formulaAl_(X1)Ga_(X2)In_(X3)As_(Y1)P_(Y2)N_(Y3)Sb_(Y4), where X1, X2, X3, Y1,Y2, Y3, and Y4 represent relative proportions, each greater than orequal to zero and X1+X2+X3+Y1+Y2+Y3+Y4=1 (1 being the total relativemole quantity). Other suitable substrates include II-VI compoundsemiconductors having a composition Zn_(A1)Cd_(A2)Se_(B1)Te_(B2), whereA1, A2, B1, and B2 are relative proportions each greater than or equalto zero and A1+A2+B1+B2=1 (1 being a total mole quantity). Furthermore,a portion or entire semiconductor substrate may be strained. Trenchisolation 110 may include any now known or later developed insulativematerial, e.g., silicon oxide. Substrate 102 and trench isolation 110may be formed using any now known or later developed techniques.

FIG. 1 also shows optionally forming a gate dielectric layer 120 oversubstrate 102. Gate dielectric layer 120 may include any now known orlater developed high-k dielectric (k equal to or >3.9) material such ashafnium silicate (HfSi), hafnium oxide (HfO₂), lanthanum oxide (LaO₂),zirconium silicate (ZrSiO_(x)), zirconium oxide(ZrO₂), silicon oxide(SiO₂), silicon nitride (Si₃N₄), silicon oxynitride (SiON), high-kmaterial or any combination of these materials. Forming as used hereinmay include any appropriate depositing technique(s) appropriate for thematerial to be deposited including but not limited to: chemical vapordeposition (CVD), low-pressure CVD (LPCVD), plasma-enhanced CVD (PECVD),semi-atmosphere CVD (SACVD) and high density plasma CVD (HDPCVD), rapidthermal CVD (RTCVD), ultra-high vacuum CVD (UHVCVD), limited reactionprocessing CVD (LRPCVD), metalorganic CVD (MOCVD), sputteringdeposition, ion beam deposition, electron beam deposition, laserassisted deposition, thermal oxidation, thermal nitridation, spin-onmethods, physical vapor deposition (PVD), atomic layer deposition (ALD),chemical oxidation, molecular beam epitaxy (MBE), plating, evaporation.

FIG. 1 also shows forming a high dielectric constant (high-k) layer 122over first-type FET 104 region and second-type FET region 106. High-klayer 122 may include but is not limited to tantalum oxide (Ta₂O₅),barium titanium oxide (BaTiO₃), hafnium oxide (HfO₂), zirconium oxide(ZrO₂), aluminum oxide (Al₂O₃) or metal silicates such as hafniumsilicate oxide (Hf_(A1)Si_(A2)O_(A3)) or hafnium silicate oxynitride(Hf_(A1)Si_(A2)O_(A3)N_(A4)), where A1, A1, A3, and A4 representrelative proportions, each greater than or equal to zero and A1+A2+A3+A4(1 being the total relative mole quantity). Dielectric layer 120 and 122may be single layer.

A metal layer 124 may be formed over high-k layer 122 and overfirst-type FET region 104 and second-type FET region 106. Metal layer124 may include, for example, elemental metals such as tungsten (W),tantalum (Ta), aluminum (Al), ruthenium (Ru), platinum (Pt), etc. or anyelectrically conductive compound including but not limited to titaniumnitride (TiN), tantalum nitride (TaN), nickel silicide (NiSi),nickel-platinum silicide (NiPtSi), titanium nitride (TiN), tantalumnitride (TaN), titanium carbide (TiC), tantalum carbide (TaC), tantalumcarbide oxynitride (TaCNO), ruthenium oxide (RuO₂), etc., and mixturesand multi-layers thereof. In any event, metal layer 124 exhibits a firsteffective work function compatible with a FET to be formed over one offirst type FET region 104 or second type FET region 106. As shown inFIG. 1, a silicon layer 126 may also be formed over metal layer 124.Conventional dual work function metal gate integration techniques would,at this point, require removal of metal layer over a selected one ofregions 104, 106 and deposition of another metal having a work functioncompatible with the FET to be formed over that selected region.

In contrast to conventional techniques, however, as shown in FIG. 2,first effective work function of metal layer 124 is changed to a second,different effective work function over the second-type FET region 106 byimplanting a species 140 into metal layer 124 over second-type FETregion 106. “Effective work function” does not necessarily meanmodulation of the metal ‘work function’, which is commonly understood tomean ‘vacuum work function’. Rather, certain embodiments may rely ondiffusion of the implanted species into the dielectric stack, insteadshifting threshold voltage by other mechanisms such as fixed charge orelectrostatic dipoles due to different electro-negativities of theelements involved. In one embodiment, one of regions 104, 106 may bemasked (first-type FET region 104 as shown) using any now known or laterdeveloped mask 130. However, a mask may not be necessary if implantingaccurate enough to cover only one of the regions is available. In oneembodiment, aluminum (Al) is used as the selected species, but otherrare earth metal species may also be employed such as lanthanum (La),iridium (Ir), platinum (Pt), ruthenium (Ru), magnesium (Mg), strontium(Sr) or barium (Ba). Silicon layer 126 (and dielectric layer 120 and/or122) may also be implanted with the species. Implanting may occur usingany now known or later developed implanting technique, e.g., beamimplant, plasma implant, etc.

FIG. 3 shows forming a first-type FET 150 compatible with firsteffective work function over first-type FET region 104 (an area outsidesecond-type region 106) and forming a second-type FET 152 compatiblewith the second effective work function over second-type FET region 106.Part of FET formation includes implanting and annealing to formsource/drain regions 160. Other processing such as forming spacers,silicide contacts, etc., has been omitted for clarity.

Implanted species 140 in high-k dielectric 122 creates a dipole betweena bottom of high-k dielectric 122 and substrate 102 such that aeffective work function of metal layer 124 is not specific to a top ofmetal layer 124 but to a bottom of high-k dielectric 122, thus shiftingthe effective work function of metal layer 124 over second-type FETregion 106. As shown in FIG. 4, species 140 may also diffuse throughhigh-k dielectric 122, e.g., during annealing that may occur as part ofsource/drain region 160 formation or other processing. Metal layer 124acts as a screen layer to prevent too much diffusion of species 140 intohigh-k dielectric 122. As indicated, silicon layer 126 absorbs some ofspecies 140. As an added benefit, species 140 implantation also acts toretard boron diffusion to a channel where second-type FET region 106 isfor a PFET.

FIG. 4 also shows a structure 170 comprising a first-type FET 150including a gate 172 having high-k layer 122 and metal layer 124, themetal layer having a first effective work function. Structure 170 alsoincludes second-type FET 152 including a gate 174 having high-k layer122 and metal layer 124, but with the metal layer further including animplanted species 140 that changes the first effective work function toa different second effective work function.

FIG. 5 shows a graph illustrating a threshold voltage shift capabilityof the methods according to the disclosure. In one embodiment, athreshold voltage shift of greater than a 50 milli-Volt shift forsecond-type FET is possible. This is a significant improvement overconventional processing during which ratios of, for example, titanium,nitride and aluminum are controlled during a reactive co-sputtering oftitanium and aluminum in a nitrogen ambient. In another embodiment, athreshold voltage shift of approximately 600 milli-Volts may be possiblesuch that the threshold voltage shift between the NFET and the PFETapproaches a band edge threshold voltage shift of the PFET.

The methods as described above are used in the fabrication of integratedcircuit chips. The resulting integrated circuit chips can be distributedby the fabricator in raw wafer form (that is, as a single wafer that hasmultiple unpackaged chips), as a bare die, or in a packaged form. In thelatter case the chip is mounted in a single chip package (such as aplastic carrier, with leads that are affixed to a motherboard or otherhigher level carrier) or in a multichip package (such as a ceramiccarrier that has either or both surface interconnections or buriedinterconnections). In any case the chip is then integrated with otherchips, discrete circuit elements, and/or other signal processing devicesas part of either (a) an intermediate product, such as a motherboard, or(b) an end product. The end product can be any product that includesintegrated circuit chips, ranging from toys and other low-endapplications to advanced computer products having a display, a keyboardor other input device, and a central processor.

The foregoing drawings show some of the processing associated accordingto several embodiments of this disclosure. In this regard, each drawingor block within a flow diagram of the drawings represents a processassociated with embodiments of the method described. It should also benoted that in some alternative implementations, the acts noted in thedrawings or blocks may occur out of the order noted in the figure or,for example, may in fact be executed substantially concurrently or inthe reverse order, depending upon the act involved. Also, one ofordinary skill in the art will recognize that additional blocks thatdescribe the processing may be added.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the disclosure.As used herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present disclosure has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the disclosure in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the disclosure. Theembodiment was chosen and described in order to best explain theprinciples of the disclosure and the practical application, and toenable others of ordinary skill in the art to understand the disclosurefor various embodiments with various modifications as are suited to theparticular use contemplated.

What is claimed is:
 1. A structure comprising: a first-type field effecttransistor (FET) including a gate having a high dielectric constant(high-k) layer and a single metal layer over a first type FET region andthe high-k layer, the single metal layer having a first effective workfunction; and a second-type FET including the high-k layer and thesingle metal layer over a second type FET region and the high-k layer,the high-k layer further including an implanted aluminum (Al) species,the single metal layer further including the implanted aluminum (Al)species that changes the first effective work function to a differentsecond effective work function resulting in a greater than 50 millivoltthreshold voltage shift for the second type FET region when compared tothe first type FET region, wherein the single metal layer is selectedfrom the group consisting of: tungsten (W), tantalum (Ta), aluminum(Al), ruthenium (Ru), platinum (Pt), titanium nitride (TiN), tantalumnitride (TaN), titanium carbide (TiC), tantalum carbide (TaC), tantalumcarbide oxynitride (TaCNO), ruthenium oxide (RuO₂), and mixtures andmulti-layers thereof.
 2. The structure of claim 1, further comprising apolysilicon layer over the metal layer in each of the first-type andsecond-type FETs.
 3. The structure of claim 1, wherein the thresholdvoltage shift is approximately 600 milli-Volts.
 4. The structure ofclaim 1, wherein the first-type FET includes an n-type FET (NFET), andthe second-type FET includes a p-type FET (PFET), and a thresholdvoltage shift between the NFET and the PFET approaches a band edgethreshold voltage shift of the PFET.
 5. A structure comprising: afirst-type field effect transistor (FET) including a gate having a highdielectric constant (high-k) layer and a single metal layer over a firsttype FET region and the high-k layer, the single metal layer having afirst effective work function; and a second-type FET including thehigh-k layer and the single metal layer over a second type FET regionand the high-k layer, the single metal layer and the high-k layer eachfurther including an implanted aluminum (Al) species that changes thefirst effective work function to a different second effective workfunction wherein a threshold voltage shift for the second-type FET isgreater than 50 milli-Volt compared to the first-type FET, wherein thesingle metal layer is selected from the group consisting of: tungsten(W), tantalum (Ta), aluminum (Al), ruthenium (Ru), platinum (Pt),titanium nitride (TIN), tantalum nitride (TAN), titanium carbide (TIC),tantalum carbide (TaC), tantalum carbide oxynitride (TaCNO), rutheniumoxide (RuO2), and mixtures and multi-layers thereof, the structurefurther comprising a polysilicon layer over the metal layer in each ofthe first-type and second type FETs, and wherein the threshold voltageshift is approximately 600 milli-Volts.
 6. The structure of claim 5,wherein the first-type FET includes an n-type FET (NFET), and thesecond-type FET includes a p-type FET (PFET), and a threshold voltageshift between the NFET and the PFET approaches a band edge thresholdvoltage shift of the PFET.